Angle of List and Angle of Loll

Question 1

Define Angle of Loll
How do you get an angle of loll?

Answer 1

The angle at which a ship with a negative initial metacentric height will lie at rest in still water

• Vessel has an initial negative GM
• An external force creates a small capsizing lever
• In the inclined state B moves outward until it is vertically under G. Vessel is at rest (Wf = Bf).
• M is not assumed to be fixed for large angles of heel.
• KM = KB + BM, (small increase in KB)
• BM = I/ V ∴ I = LB³/12
• Moment of inertia of the W.P.A increases therefore BM increases.
• As the waterline beam of the vessel increases M effectively rises above G.

Question 2

Define List
What has happened to G?

Answer 2

A ship that is in an inclined condition due to the distribution of weights within it.

G has shifted transversely off the centre line in the direction of weight that has been shifted.

Question 3

How do you correct for an angle of Loll?

Answer 3

• You need move G down to bring it below M.
• Try to keep it close to the centreline to avoid increasing the list/capsizing moment.
  -Ballast the tanks 1 at a time to minimise FSM.

Question 4

How does G move when a weight is loaded?

Answer 4

G moves directly towards the weight loaded.

Question 5

How does G move when a weight is shifted?

Answer 5

G moves parallel and in the same direction as the weight shifted.

Question 6

How does G move when a weight is discharged?

Answer 6

G moves directly away from the weight discharged.

Question 7

How do you calculate how to bring a vessel to even keel when they have a list to port or to starboard?

Answer 7

Moments to port = moments to starboard
w x s = w x s

Question 8

Procedures and Precautions when attempting to correct a large angle of list

Answer 8

Determine cause
Bilging
Shift of cargo
Valves failing or left open
Asymmetric ice accretion
Watertight Integrity compromised
Operator error

Correct Cause
Bring G back to the CL without making the vessel unstable, over stressing the vessel or compromising freeboard

Ballast - GM will initially reduce if filling an empty compartment

Add weight to the high side
discharge weight from the low side
Transfer weight from low side to high side

Question 9

How to determine if a vessel is at a an angle of loll or angle of list?

Answer 9

Determine cause of heel
Bilging
Shift of cargo / loss of cargo
Valves failing / left open
Watertight integrity compromised
Picking up / shifting heavy weight
TDC absorption of moisture
Ice accretion, symmetrical or asymmetrical
Operator error during ballasting / deballasting

Observe draught Determine KM

Sound round the vessel all tanks including voids
Account for any unexpected results.

Calculate the vessels KG (to establish the vessel’s condition of equilibrium) and TCG.
GM positive (or possibly zero) listed
GM negative loll
GM negative / TCG ≠ 0 Loll plus list.